%0 Journal Article %J J Immunol %D 2004 %T B7 expression on T cells down-regulates immune responses through CTLA-4 ligation via T-T interactions [corrections]. %A Taylor, Patricia A %A Lees, Christopher J %A Fournier, Sylvie %A Allison, James P %A Sharpe, Arlene H %A Blazar, Bruce R %K Animals %K Antigen-Presenting Cells %K Antigens, CD %K Antigens, CD80 %K Antigens, CD86 %K Antigens, Differentiation %K Bone Marrow Transplantation %K CD4-Positive T-Lymphocytes %K Cell Communication %K CTLA-4 Antigen %K Down-Regulation %K Graft vs Host Disease %K Ligands %K Lymphocyte Activation %K Membrane Glycoproteins %K Mice %K Mice, Inbred BALB C %K Mice, Inbred C57BL %K Mice, Transgenic %K Receptors, Interleukin-2 %K T-Lymphocyte Subsets %K Up-Regulation %X Although B7 on APCs has a well-recognized role in T cell costimulation, little is known about the functional significance of constitutive and activation-induced B7 expression that also occurs on T cells. To analyze the role of B7 on T cells, B7-1/B7-2-deficient mice (B7 double knockout) and mice overexpressing B7-2 exclusively on T cells (B7-2 transgenic) were used as T cell donors for allogeneic transplant recipients, and graft-vs-host disease (GVHD) was assessed. B7 double-knockout T cells resulted in significant GVHD acceleration compared with wild-type T cells. Conversely, B7-2 transgenic donor T cells mediated reduced GVHD mortality compared with wild-type T cells. Data indicated that B7 expression on T cells down-regulated alloresponses through CTLA-4 ligation. This study is the first to provide definitive in vivo data illustrating the importance of T cell-associated B7 as a negative regulator of immune responses in a clinically relevant murine model of GVHD. The up-regulation of B7 on T cells may be an important component of normal immune homeostasis. %B J Immunol %V 172 %P 34-9 %8 2004 Jan 1 %G eng %N 1 %1 http://www.ncbi.nlm.nih.gov/pubmed/14688306?dopt=Abstract